39 replies to this topic

[moxican]

I have been using the Skywatcher AZ-Gti for about a month now, and although initially it was pretty good, it has developed a significant amount of backlash on its declination axis. This is a well documented subject on CN. So, against all odds and other people suggestions on CN to just leave with it, I had to find a way to make it at least more acceptable. That is just the way I am built.

Thus, I am making this tutorial on how I did it. It will require patience and I'd say intermediate tinkering skills. Make sure you understand that you do this at your own risk!!! You break something the mount is finished. I'd say the entire endeavor took me somewhere between 2-3 hours, but I am quite handy.

 

Tools you will need:

- a mid to large size flat screwdriver

- a small flat screwdriver

- 1.5 mm (metric) Allen key (hex key)

- a small Philips screwdriver, it needs to be able to reach into small holes to about 1/2 - 3/4 inch

- optional - some machinery grease

- favorite drink

 

The very first thing you want to do is to disconnect your mount from any power source. If you use a 12V battery make sure it is unplugged from the mount, if you use batteries remove them all!

Second thing, untwist the declination knob all the way until it comes separate from the mount. From here on you will void the warranty of your SW mount.

There are six fairly small screws that hold the black plastic cover onto the white metal housing. You need to remove this plastic cover in order to gain access to the inside of the mechanics so go ahead and remove them. I have marked them on the following images.

 

 

 

Now, carefully remove the plastic, there are wires running to it. You don't want to break any of these cables!!! On the inside you will see two large gears, one for the declination and one for the right ascension axis on each side of the mount along with their motor drive unit. After some investigation and trial and error, I found out that contrary to the belief out there the issue is not located between the declination gear and its driving gear. Its location is in the motor unit's gearbox. See attached image...

 

 

To illustrate the amount of backlash that was in the gearbox, click on this link. It is a considerable amount and something PHD2 was unable to cope with... understandably.

Edited by moxican, 16 July 2019 - 12:51 AM.

[moxican]

In order to successfully fix this issue, the entire motor control unit has to be removed. I have marked the bolt and screws that needs to be dealt with.

 

 

Screw# 1 is optional to take out. It is responsible for having spring loading the control box to the declination gear. The spring hook can simply be unhooked and re-hooked. It is a bit of a pain in the a** to put it back.

Screw#2 is really a bolt and a screw. Make sure you loosen the bolt first! The screw inside the bolt is very brittle and if you break off the top slit, you will have no way of working with it. I am not sure what size is the bolt, it is not really tight, I used a small pliers to remove it. When this is done, you want to make sure you remove that inside screw as well, that the bolt was hanging onto. You keep unscrewing and it will come loose eventually.

Screw# 3 is just a screw to fix the other end of the unit to the declination gear. In fact perhaps it's best to remove this screw before you remove screw# 2. Your choice on this one.

 

The entire motor drive unit is loose but don't just yank it out yet. You have to disconnect it's power cable first. It is just a simple but careful pull.

 

 

 

Now you have the unit to work with. In order to make the necessary adjust to the gearbox, you need to remove the main gear that is fixed to the end of the motor axle. Both gears will have two small hex screws to hold them tight to their axes. I have made two yellow marks. I circled the hex screw which needs to be found on the gear the arrow points to. The arrow also points to the service openings to have access to these hex screws. You will need a 1.5 mm Allen key for this move. If the screw do not line up with the service holes you can turn them by rotating the small plastic gear on the other end of the entire unit. You don't have to remove the gear on the drive axle for the large declination gear.

 

 

 

 

Attached Thumbnails

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[moxican]

After removing the small gear, you will see three small screws right under it. These screws are the one that hold the metal housing of the drive unit together.

 

 

You need to loosen all three screws (no need to take them out completely), and push the frame downward shown as an arrow on the picture. This will ensure that the two gears will lock together tight and won't have that play that I have shown on the first post. Once you have done adjusting the frame, hold it there until you fasten all three screws back again. From here on you just simply track your steps backward, and re-assemble everything. Just look at how tight the gears are after I put the gear back on mine!

 

 

This last step is more of a suggestion. I decided to put some automotive grease on the gears. Hear in Canada we get some pretty cold winters and the factory grease Skywatcher put on becomes sticky and rigid in those frigid temperatures. 

 

 

I did not remove the gear box for the RA axis as the backlash there is minimal, but if that is something you need to tune up as well, same steps apply

 

Unfortunately I did not have a chance to test it under a star studded night. Clouds are so dark here tonight I don't know if the Sun will be able to penetrate tomorrow morning, but that is how usually go when you want to test equipment around here  . But I did try it out indoors with camera and slowest slewing speed, and it looks very promising. Backlash is noticeably less then it was before the tune up. I want to put PHD2 on it and test the hell out of it to see how it performs.

Edited by moxican, 16 July 2019 - 12:57 AM.

[tkottary]

Thank you for this! 

[Michal Juul]

It's a really good tutorial. Thank you so much 

[DIMITRIS K.]

Wow! My congrats for your tutorial. I'll try this to my mount to see if i have any more improvement! 

[trurl]

  

[moxican]

No problem gentlemen. Make sure that before you put the final plastic cover back on the mount you test the gears and make a full rotation of the adjusted axis, in my case the declination. Do it at highest speed and listen to the mechanics. If you hear at any point that the motor is exerting more power to keep turning or it is getting out of "breath", you have to loosen the tension adjustment. You gears are binding up there. 

[Biggen]

This is great. I’m going to try this I think this weekend.

 

Great job. Be sure to report back when you try guiding with PHD2 again.

[Bowlerhat]

Thank you, this is helpful. Last time I used it I got backlash as well, might need to open it up.

[DIMITRIS K.]

Yesterday i was trying to fine adjust my mount. My problem is that when i'm trying to correct a backlash in the first half of the mount as it rotates, i get a gear tension in the other half and i head the motor struggle and vice versa. This is minimal without load, but it's obvious with all my gear loaded on the mount. The best i manage to do is to find a balance between those two. I have a little backlash on the first half and little tension on the other half. But as mutch as i try, i can't find a "sweet spot" to eliminate both. Do you experience the same problem?

[moxican]

I did not see any tension on mine. One thing you need to know though, the quality on this mount varies wildly. Some people report absolutely no backlash, other people report so much of it that they can barely use it for visual observation. 

I have adjusted mine and although it has gotten better it is still too large for PHD2 to deal with. Those of us who tried to contact Skywatcher got the "it is supposed to be like that" reply and a disclaimer that they have never design this for astrophotography.

[DIMITRIS K.]

My first mount had a lot of issues. Tracking was so bad that i didn't manage to get a picture from Sharpcap without star trails. I' ve managed to get an acceptable tracking from time to time but then i had a lot of wi fi disconnections. And go to was too far away from target all the time. I've returned it to my vendor and had a replacement with a brand new, that  i use  now. This mount is way better from the first one, but sometimes i struggle again with tracking issues. I must play with the arrow keys to make it track right, but i' ve managed to do a 5 minute stacking without significant problems. It seems to need a "push" for the gears to engage right. Skywatcher must reconsider it's quality control with that one. But i suspect it had desing flaws that must improve with a second revision. Too bad that i can't use it for imaging, because it's small and super easy to setup for some quick low exposures and i must rely on my perfect but time consuming to setup and run SXD2 for that. Maybe i asked too much for this price tag, but if it's working right from time to time, why not working right all the time? 

Edited by DIMITRIS K., 19 July 2019 - 04:21 PM.

[moxican]

My first mount had a lot of issues. Tracking was so bad that i didn't manage to get a picture from Sharpcap without star trails. I' ve managed to get an acceptable tracking from time to time but then i had a lot of wi fi disconnections. And go to was too far away from target all the time. I've returned it to my vendor and had a replacement with a brand new, that  i use  now. This mount is way better from the first one, but sometimes i struggle again with tracking issues. I must play with the arrow keys to make it track right, but i' ve managed to do a 5 minute stacking without significant problems. It seems to need a "push" for the gears to engage right. Skywatcher must reconsider it's quality control with that one. But i suspect it had desing flaws that must improve with a second revision. Too bad that i can't use it for imaging, because it's small and super easy to setup for some quick low exposures and i must rely on my perfect but time consuming to setup and run SXD2 for that. Maybe i asked too much for this price tag, but if it's working right from time to time, why not working right all the time? 

Well, based on what you just said here, which I've heard from other users as well, it is unfit for visual use as well. Quality control would be the culprit, but that is too much of an expectation from Skywacther, it's a Chinese company, they just won't care.

And lastly, no... you are not expecting too much from that price tag. You'd be if it cost $100.

[charlieb123]

Thank you for the information moxican. Truly appreciated.

 

I was having sticking issues with the Azimuth axis on my AZ-GTI so I decided to take it apart and adjust motor backlash while I was in there.

As lightly as I tried to remove the slotted screw I ended up breaking off one of the "tabs" of the slot.

 

To resolve this I threaded on a pair of nuts and locked them together. I was then able to remove the screw with a socket.

While I could make another screw I decided to use the existing one with the nuts in place. By using a thicker washer I was able to set the preload to where it should be.

 

So there you go, if you break yours don't fret, there is a way to fix it. The only way I see this going bad is if you were to snap the stud when locking down the nuts or removing it.

Worst case you could remove the encoder disk cover which would allow you to pull the motor mount off the stud. You would then have full access to the stud allowing you to remove it with pliers.

 

After adjusting the motor backlash and re-greasing the AZ axis no longer sticks during use.

 

It's unfortunate the AZ axis and clutch adjustment isn't as smooth as the Declination axis. Seems to work okay but it sticks more than the DEC axis resulting in it feeling inferior.

 

Edited by charlieb123, 02 August 2020 - 10:26 AM.

[moxican]

Thank you for the information moxican. Truly appreciated.

 

I was having sticking issues with the Azimuth axis on my AZ-GTI so I decided to take it apart and adjust motor backlash while I was in there.

As lightly as I tried to remove the slotted screw I ended up breaking off one of the "tabs" of the slot.

 

To resolve this I threaded on a pair of nuts and locked them together. I was then able to remove the screw with a socket.

While I could make another screw I decided to use the existing one with the nuts in place. By using a thicker washer I was able to set the preload to where it should be.

 

So there you go, if you break yours don't fret, there is a way to fix it. The only way I see this going bad is if you were to snap the stud when locking down the nuts or removing it.

Worst case you could remove the encoder disk cover which would allow you to pull the motor mount off the stud. You would then have full access to the stud allowing you to remove it with pliers.

 

After adjusting the motor backlash and re-greasing the AZ axis no longer sticks during use.

 

It's unfortunate the AZ axis and clutch adjustment isn't as smooth as the Declination axis. Seems to work okay but it sticks more than the DEC axis resulting in it feeling inferior.

 

screwstud-1.jpg

Charlie, I have gotten the same issue back then. I have resolved it with a needle nose plier gripping the one half that was left behind, and turned it very carefully. But this is a great idea, thanks.

Do you use this mount for AP at all or strictly observing?

[charlieb123]

Charlie, I have gotten the same issue back then. I have resolved it with a needle nose plier gripping the one half that was left behind, and turned it very carefully. But this is a great idea, thanks.

Do you use this mount for AP at all or strictly observing?

Hi Moxican,

I just got into this expansive world of astronomy and am using the mount for AP.

Quite a learning curve to understand all the aspects necessary for AP just to attempt to take photos with exposures longer than 20 seconds.

Wrapping my flexi tripod around the railing of my deck and taking 15 second exposures was a lot easier than setting up and using an AP rig.
Along with:

How to mount your lens/scope and camera.

How to get the mount connected to your computer.

How to get the camera connected to your computer.

How to polar align.

How to know what star you're pointing at.

What software to use and how to use it.

How to focus.

How to make your own FTDI adapter.

How to build your own DIY focuser.

How to deal with dew.

and so much more!

 

With all that said, I'm enjoying it.

Thanks again for your how to. The information is appreciated for those of us who like to take things apart without destroying them.

Edited by charlieb123, 03 August 2020 - 11:47 AM.

[dicksonfu]

How much the slotted bolt and the nut on both sides of worm gear assembly should be tightened?

I wonder if the tighteness of them can affect the play of the worm gear and thus the backlash.

[andysea]

I tried to remove backlash in one of those mounts. The issue that I ran into is that the backlash isn’t actually between the worm and the wheel. Most of the backlash is generated by the planetary reducing gears. I took completely apart those reducers. There is no way to remove their backlash. The only solution would be to replace those gearboxes with higher quality ones. The stock ones are pretty bad.

[Cometeer]

I tried to remove backlash in one of those mounts. The issue that I ran into is that the backlash isn’t actually between the worm and the wheel. Most of the backlash is generated by the planetary reducing gears. I took completely apart those reducers. There is no way to remove their backlash. The only solution would be to replace those gearboxes with higher quality ones. The stock ones are pretty bad.

I came to the same realization this weekend. The little motor shaft wiggles around a bit, causing backlash. Found no way to fix it. 

[andysea]

I don’t think there is a way. The only solution is to replace the gearboxes. I have a paper which is an engineering analysis of this mount. The cheap gearboxes were mentioned as a poor choice.

Edited by andysea, 13 August 2020 - 07:10 PM.

[dicksonfu]

Could you able to share the research paper?

[andysea]

Here is the link. 

https://www.scribd.c...ywatcher-AZ-Gti

I had to sign up in order to read it.

[Knobby]

How much the slotted bolt and the nut on both sides of worm gear assembly should be tightened?

I wonder if the tighteness of them can affect the play of the worm gear and thus the backlash.

Great question ! I've wondered myself if the nuts should lock the position of worm or just allow slight movement.

[SkyArcher]

There is a set screw that adjusts the play in the worm gear / main gear under one of the screws next to the spring.